Both Staples (NASDAQ:SPLS) and Costco (NASDAQ:COST) disappointed investors this quarter, but one key difference here separates a long-term performer from a company that could be in serious trouble. While Costco reported a 15% decline in profits, its third-straight quarter of underperforming expectations, Motley Fool analyst Bill Mann says, in this segment from Thursday's Investor Beat, that the company draws its real revenue from its membership model, and that this is a business that is still very strong at the moment. Meanwhile, with Staples announcing that it will be closing 10% of its North American stores, the situation for this company could be much more dire.